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Search for diffuse extraterrestrial contained neutrino-induced cascades using IceCube
79- and 86-string configurations
Mariola Lesiak-Bzdak Stony Brook University for the IceCube Collaboration
Outline: • Motivation • Analysis Method • Unblinded Events • Summary
Geographic South Pole"
Amundsen-Scott "South Pole Station"
1
IceCube detector
07 April 2014, APS Meeting, Savannah, Georgia
Search for a Diffuse Neutrino Flux
2
Diffuse Flux = effec&ve sum of neutrino fluxes from all extraterrestrial sources (e.g. AGNs) • Signal:
– Extraterrestrial ν from ~E-2
sources • Background:
– Atmospheric µ – Atmospheric ν (conven&onal from
π/K and prompt from charmed mesons)
• Sensitive to all three ν flavors • Energy information used to
separate signal from background
Mariola Lesiak-‐Bzdak, APS 2014
Northern sky
Southern sky
GRBs AGNs Energy
Atmospheric ν, µ Harder
Spectrum ν (E-2)
Neutrino Event Signatures
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νμ N è μX
Color coding: red – earliest blue -‐ latest
Mariola Lesiak-‐Bzdak, APS 2014
νe Nè cascade
Cascade (data)
Tracks with length ~1km
§ angular resolution <1o
§ energy resolution log(E) ~ 0.2
€
νµ +N→µ + XN -‐ target nucleon X -‐ hadronic shower
νµ (CC)
Track (data)
This Analysis Cascades § e-m and hadronic cascades
§ energy resolution ~ log(E)~0.04 (above 10 TeV) § angular resolution: ~8 degree
€
νe(τ ) + N →e(τ ) + Xν l + N →ν l + X l = e, µ,τ
νe(τ)(CC) νl(NC)
IceCube Contained Cascade Analyses
• Neutrino-‐Induced Contained Cascade Searches in IceCube based on Monte Carlo background simula&ons: – IC22-‐strings (published PRD84 (2011) 072001) – IC40-‐strings (accepted to PRD arXiv:1312.0104) – IC59-‐strings (preliminary, ICRC2013 proceedings arxiv:
1309.7003)
– IC79+IC86 – this analysis
4 Mariola Lesiak-‐Bzdak, APS 2014
IceCube detector string configura&on growth: IC9 = 9 strings (2006) IC22 = 22 strings (2007) IC40 = 40 strings (2008) IC59 = 59 strings (2009) IC79 = 79 strings (2010) IC86 = 86 strings (2011)
IC22 data events
IC40 data events
IC59 data events
E=40 TeV E=51 TeV
Mariola Lesiak-‐Bzdak, APS 2014 5
Search for Contained Cascades in IceCube with 79- and 86- strings
• Signal: Extraterrestrial ν e CC and (ν e + ν µ) NC from ~E-2 sources
• Background: Atmospheric µ and ν µ CC • Analysis Strategy:
– Demand spherical light distribution pattern and its reconstructed vertex to be contained inside the detector volume
Mariola Lesiak-‐Bzdak, APS 2014 6
Search for Contained Cascades in IceCube with 79- and 86- strings
• Signal: Extraterrestrial ν e CC and (ν e + ν µ) NC from ~E-2 sources
• Background: Atmospheric µ and ν µ CC • Analysis Strategy:
– Demand spherical light distribution pattern and its reconstructed vertex to be contained inside the detector volume
– Combina&on of quality cuts on different variables op&mized using Monte Carlo background simula&ons
– Selec&on criteria developed on 10% of the data
Example of Cascade Variable
TimeSplitPosi&on= difference between the reconstructed vertex posi&ons reconstructed for each event half
Selected events TimeSplitPosi?on
Mariola Lesiak-‐Bzdak, APS 2014 7
Search for Contained Cascades in IceCube with 79- and 86- strings
• Good data vs Monte Carlo shape agreement • Good data vs Monte Carlo rate agreement
Data vs MC rate agreement at different cut levels
Reconstructed Zenith
Example of Data/MC shape agreement
• Energy range between 13 TeV and 5.3 PeV
• Signal efficiency (final to trigger level) ~30% up to 3.5 PeV
• Vertex resolution ~4 m • Energy resolution: ~9% • Angular resolution: ~8 degrees • Purity (νAstr/(μ+νAtm+νAst)):
– E>10TeV: 37% – E>60 TeV: 83%
• Muon Contamination (μ/(νAtm+νAst+μ)): – E>10TeV: 8% – E>60 TeV: 0.5%
Contained Cascades in IC79+IC86
8 Mariola Lesiak-‐Bzdak, APS 2014
Conv. norm. (Honda+H3a) = 1.0 Prompt norm. (ERS+H3a) = 1.0 Astro. Norm. (10-‐8E-‐2) = 1.0 Honda = Honda et al., PRD 75 (2007) H3a = Gaisser, Astropart. Phys. 35 (2012) ERS = Enberg et al., PRD 78 (2008)
Reconstructed energy ager final event selec&on (10% of the data)
Sta&s&cal uncertain&es only
Effective Area in Contained Cascades Search
9 Mariola Lesiak-‐Bzdak, APS 2014
IC79 Effec&ve Area
Factor of ~1.5 improvement
NuE
Comparison of Effec&ve Area for IC79 and IC59 Contained Cascades
Black Points = Toy Data MC
Likelihood Fit Test
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Input values: Conv. norm. (Honda+H3a) = 1.0 +/-‐ 0.5 Prompt norm. (ERS+H3a) = 1.0 Astro. Norm. (10-‐8E-‐2) = 1.0 Energy Scale = 1.00 +/-‐ 0.15
Mariola Lesiak-‐Bzdak, APS 2014
Toy MC LLh fit results for 1000 samples of toy Data MC
Honda = Honda et al., PRD 75 (2007) H3a = Gaisser, Astropart. Phys. 35 (2012) ERS = Enberg et al., PRD 78 (2008)
Physics Goal: perform likelihood fit to the 2-‐yr energy distribu&on and extract contribu&on of astrophysical E-‐2 normaliza&on
• Toy Data MC results: – Expected uncertainty on astrophysical
E-‐2 normaliza&on of ~35% – All-flavor sensitivity: E2Φ90%CL < 0.90 x
10-‐8E-‐2GeV-‐1s-‐1sr-‐1cm-‐2
IC79+IC86 Contained Cascades vs HESE* analysis
Mariola Lesiak-‐Bzdak, APS 2014 11
HESE Analysis
• Select cascades • Background es&mated from Monte
Carlo simula&ons • Contained cascade search above E>10
TeV (Total Charge>300 P.E.)
• Select tracks and cascades • Background es&mated from data • Contained cascade and tracks search
at high energies (Total Charge>6000 P.E. àEnergy ~ 30 TeV)
IC79+IC86 Contained Cascades
ν
μ
ν
Veto
μ
*High Energy Star&ng Events (Science 342, 1242856 (2013))
Effective Area of Contained Cascades vs HESE
12 Mariola Lesiak-‐Bzdak, APS 2014
• Below 150 TeV effec&ve area bigger than in HESE analysis
• Same effec&ve area above 150 TeV -‐ 3 PeV as in HESE analysis
Spatial Distributions of Unblinded IC79+IC86 Contained Cascades
IC79+IC86 unblinded events
13
Events well contained in the detector volume
Black dots denote IceCube strings loca&on
Mariola Lesiak-‐Bzdak, APS 2014
Vertex Posi&on X [m]
Vertex Posi&on
Y [m
]
Distance to the central string in IceCube [m] Ve
rtex Posi&on
Z [m
]
IC79 Unblinded Events E>60 TeV (3 events)
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E=114.2 TeV E=99.7 TeV E=64.2 TeV
Mariola Lesiak-‐Bzdak, APS 2014
IC79 Unblinded Events E>60 TeV (3 events)
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E=114.2 TeV E=99.7 TeV E=64.2 TeV
Mariola Lesiak-‐Bzdak, APS 2014
These events not in HESE sample (Science 342, 1242856 (2013))
IC86 Unblinded Events E>60 TeV (10 events)
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120.3 TeV 183.1 TeV
119.4 TeV
1. PeV 1.1 PeV
99.7 TeV 68.2 TeV 67.2 TeV
Events overlaping with HESE (Science 342 (2013) 1242856) Events not overlaping with HESE
200.2 TeV
71.7 TeV
Mariola Lesiak-‐Bzdak, APS 2014
Summary • Search for diffuse neutrino-‐induced contained cascades in
IceCube data with 79-‐ and 86-‐strings – Background es&mated from Monte Carlo simula&ons – Energy range between 13 TeV and 5.3 PeV
• Studies of the likelihood fit using toy data Monte Carlo: – Expected uncertainty on astrophysical E-‐2 normaliza&on of ~35% – Expected sensi&vity of E2Φ90%CL < 0.90 x 10-‐8E-‐2GeV-‐1s-‐1sr-‐1cm-‐2
• 2-‐year data sample unblinded: – Total of 138 events observed
• 13 events (all cascade-‐like) have reconstructed energy above 60 TeV (40% overlap with HESE analysis, 8 addi&onal cascade events)
• Stay tuned for likelihood fit results!
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BACKUP SLIDES
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Correlation Plots of the Best Fit Values
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Correla&on plots of the best fit normaliza&on values for LLh fit to the toy data MC (shown on slide 10) Input values: Conv. norm. (Honda+H3a) = 1.0 +/-‐ 0.5 Prompt norm. (ERS+H3a) = 1.0 Astro. Norm. (10-‐8E-‐2) = 1.0 Energy Scale = 15%
Mariola Lesiak-‐Bzdak, APS 2014
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